I. Field of the Invention
The present invention relates to telecommunications, and more particularly to power allocation and rate control.
II. Description of the Related Art
Wireless communications systems employ a number of geographically distributed, cellular communication sites or base stations. Each base station supports the transmission and reception of communication signals to and from stationary or fixed, wireless communication devices or units. Each base station handles communications over a particular region commonly referred to as a cell/sector. The overall coverage area for a wireless communications system is defined by the union of cells for the deployed base stations. Here, the coverage areas for adjacent or nearby cell sites may overlap one another to ensure, where possible, contiguous communications coverage within the outer boundaries of the system.
When active, a wireless unit receives signals from at least one base station over a forward link or downlink and transmits signals to at least one base station over a reverse link or uplink. Several approaches have been developed for defining links or channels in a cellular communication system, including, for example, TDMA (time-division multiple access), and CDMA (code-division multiple access).
In TDMA communication systems, the radio spectrum is divided into time slots. Each time slow allows only one user to transmit and/or receive. Thusly, TDMA requires precise timing between the transmitter and receiver so that each user may transmit their information during their allocated time.
In CDMA communications systems, different wireless channels are distinguished by different channelization codes or sequences. These distinct channelization codes are used to encode different information streams, which may then be modulated at one or more different carrier frequencies for simultaneous transmission. A receiver may recover a particular stream from a received signal using the appropriate code or sequence to decode the received signal.
For voice applications, conventional cellular communication systems employ dedicated links between a wireless unit and a base station. Voice communications are delay-intolerant by nature. Consequently, wireless units in wireless cellular communication systems transmit and receive signals over one or more dedicated links. Here, each active wireless unit generally requires the assignment of a dedicated link on the downlink, as well as a dedicated link on the uplink.
With the explosion of the Internet and the increasing demand for data, resource management has become a growing issue in cellular communication systems. Next generation wireless communication systems, such as those employing High Speed Downlink Packet Access (“HSDPA”), are expected to provide high rate packet data services in support of Internet access and multimedia communication. Unlike voice, however, data communications may be potentially bursty yet relatively delay tolerant. Data communications, as such, may not require dedicated links on the downlink or the uplink, but rather enable one or more channels to be shared by a number of wireless units. By this arrangement, each of the wireless units on the uplink competes for available resources. Resources to be managed in the uplink include the received power at the base station, and the interference created by each user to other users in the same sector or cell, as well as in other sectors or cells, for example.
Various implementations have been examined for HSDPA systems. One such scheme is orthogonal frequency-division multiple access (“OFDMA”). In OFDMA implemented HSDPA systems, a carrier signal may be defined by a number (e.g., 1024) of sub-carriers or tones transmitted using at set of mathematically time orthogonal continuous waveforms. One example of a set of orthogonal waveforms is the set of sinusoids with frequencies that are integer multiples of a fixed positive value. The orthogonality of the tones allows for their transmission and/or reception, while preventing them from interfere with one another. A number of neighboring tones may be grouped together to form a block of tones such that each user may be assigned one or more blocks of tones. Each tone experiences flat fading with respect to the other tones, and thusly, the equalization demands in the transmission and/or reception of the block of tones may be substantially reduced.
In HSDPA systems, the base station may need to manage its resources on the downlink. These base station resources include transmit power budget. OFDMA may support a simplified implementation for managing a base station's transmit power budget. In an optimized HSDPA system employing OFDMA, the transmit power budget may be uniformly allocated. Here, the transmit power allocated to each wireless unit requesting HSDPA service in an identical manner.
Once the transmit power has been allocated, the base station controls the rate of transmission for each wireless unit. In an OFDMA implemented HSDPA system, this process may involve transmitting one or more pilot signals to each wireless unit. After receiving the pilot signal(s), each wireless unit transmits a signal containing channel condition information to the base station. The channel in which the block(s) of tones are transmitted on the downlink is characterized here by this signal, more commonly referred to as channel quality information (“CQI”). More particularly, a single CQI is transmitted to the base station irrespective of the number of blocks of tones a wireless unit may have designated thereto. The base station, in response to receiving a CQI from each wireless unit, controls rate of transmission for the relevant wireless units. The number of blocks designated to a user may be reflective of the data demands of the user and the capacity of the system.
OFDMA implemented HSDPA systems have not, to date, been optimized. As a single CQI is transmitted without regard to the number of blocks of tones the wireless unit has assigned, one issue of significance is fading. One wireless unit may receive a number of blocks, each of which may fade at differing degrees. Consequently, the single CQI may not reflect changes in the channel condition over the course of time in which the numbers of blocks are transmitted on the downlink. This diminishes the gain that may be achieved by managing the base station's transmit power budget.
As a result of the hereinabove, a demand exists for a method that managing the transmit power budget and the transmission control rate of a base station. Moreover, a need exists for a method of optimizing a base station's resources for an OFDMA implemented HSDPA system.